The present invention relates to a method for forming undercuts of a metal injection molded product and metal injection molded products with undercuts.
In orthodontics, an orthodontic apparatus such as brackets are directly bonded to the teeth normally by the use of adhesive or the like. Force is applied to the brackets by an orthodontic archwire, and the teeth are forcefully aligned in an appropriate position thereby.
Therefore, various proposals have been made so as to provide sufficient bonding strength to firmly hold an orthodontic apparatus in orthodontic treatment.
As one proposal thereof, undercuts, for instance, are provided on the bonding surface of an orthodontic apparatus to teeth. By providing undercuts, the area of the bonding surface increases, and the bonding strength increases, since there is an improvement in the holding power of the dental adhesive.
Methods of providing undercuts to a bonding surface described above include a method of forming undercuts by machining or the like as secondary work after manufacturing an orthodontic apparatus body, a method of fixing wire mesh to an orthodontic apparatus body by welding or the like, and so on.
However, according to the method of carrying out the above-noted secondary work, as an orthodontic apparatus is generally relatively small, there are problems such as extremely complex working, inferior productivity and high cost.
Moreover, a strong metal such as titanium is used for orthodontic apparatuses, so that the workability is poor and undercuts are extremely hard to form. Also, in the method of bonding the wire mesh by welding or the like, there is the problem that the mesh portion is buried by brazing filler metal during welding, and the bonding force between the wire mesh and the body gradually decreases.
On the other hand, orthodontic apparatus bodies have been recently manufactured by metal injection molding that have high yield, are flexible in molding shapes and can easily mold even complex shapes. Such an metal injection molding method is used for producing a metal body by debinding and sintering after injection-molding a feed stock mainly of metal powder and binding resin.
With such a metal injection molding method, one-body molding even into a complex shape is possible, but since a mold is used for injection-molding, undercuts cannot be directly molded without carrying out the secondary work to the sintered body.
The objective of the present invention is to provide a method for forming undercuts of a metal injection molded product by means of a simple process without the need for secondary work, and to provide metal injection molded products having undercuts.
(1) A method for forming undercuts of a metal injection molded product according to the first invention comprises the steps of:
injection-molding a feed stock containing metal powder and binding resin;
forming undercuts to an injection green body provided by the injection molding; and
sintering the injection green body having undercuts after debinding.
(2) It is preferable that the undercuts are formed by deforming at least one part of the injection green body.
(3) It is preferable that the undercuts be formed by heating and softening the injection green body.
(4) It is preferable that the undercuts be formed by pressing at least one part of the injection green body with a pressing member.
(5) It is preferable that the pressing surface of the pressing member be heated.
(6) It is preferable that the temperature of the pressing surface be 90xc2x0 C. to 150xc2x0 C.
(7) It is preferable that protrusions be formed on the pressing surface of the pressing member.
(8) It is preferable that pressing be carried out a plurality of times.
(9) It is preferable that pressing be carried out while changing the shape of the pressing surface.
(10) A method for forming undercuts of a metal injection molded product according to a second invention comprises the steps of:
injection-molding a feed stock containing metal powder and binding resin;
debinding an injection green body-molded by the injection-molding; and
sintering a brown body provided by the debinding; wherein the injection green body is integrated with an undercut molding member in one body.
(11) It is preferable that the undercut molding member comprise a removable material by heating.
(12) It is preferable that the undercut molding member comprise a removable material in the debinding step.
(13) It is preferable that the undercut molding member comprise a material having resin as a main component.
(14) It is preferable that the resin have a melting point of 150xc2x0 C. to 400xc2x0 C.
(15) A method for forming undercuts of a metal injection molded product according to a third invention comprises the steps of:
injection-molding a feed stock containing metal powder and binding resin; and
sintering an injection green body molded by the injection-molding after debinding;
wherein a mold for injection-molding which has a core for forming undercuts in the mold is used in the injection-molding step.
(16) It is preferable that the core is made up of an elastic material.
(17) It is preferable that the elastic material have a Vickers hardness of 40 to 100.
(18) It is preferable that the elastic material has tensile strength of 60 Kg/cm2 or above.
(19) It is preferable that the elastic material consists of silicone rubber.
(20) It is preferable that a metal injection molded product of the preset invention be manufactured by the methods described in the above-noted items (1) or (19).
(21) It is preferable that the metal injection molded product be an orthodontic apparatus.
(22) It is preferable that the undercuts be provided to the tooth-bonding surface of the orthodontic apparatus.